1. Field of the Invention
The invention relates to a wellbore treatment process wherein the wellbore is utilized for injection or disposal of a fluid into a subterranean formation.
2. Description of Related Current Art
Injection and disposal wells are utilized throughout the world to reinject produced waters from hydrocarbon recovery to systematically enhance recovery of those hydrocarbons by volumetric production of re-injected waters as well as to maintain pressure on those producible zones. Disposal wells are utilized to dispose of liquid wastes into an underground containment reservoir. An injection well is typically constructed as follows:
A surface string is usually run from the surface through all fresh water reservoirs for protection. Many older wells do not have protective pipe all the way through known fresh water zones. Inside of the surface string is a production string of pipe which is typically 7", 51/2", or 41/2" diameter steel casing pipe. This production string is run from the surface to the production zone. The casing is cemented in place. This casing is then perforated to allow fluid injection/disposal into that formation. An injection string of tubing typically 21/2" is then run into the well inside of the production casing. A packer is connected to this tubing and is used to isolate or "pack-off" the injection interval. Pressure from injection will remain below this packer and on the inside of the tubing string. The annulus therefore will have no pressure during normal injection/disposal operations. A wellhead connection is utilized at the surface to hang the tubing and hold tension on the injection packer below. The wellhead typically has two (2) two-inch female pipe connections for access to the annulus each located 180.degree. to one another. The top of the wellhead is designed to accept the tubing and contains slips to hang the tubing from. A flat plate lays on top of the slips and inside of the wellhead. A rubber packing ring is then placed on top of this plate with another ring laid on top of the rubber for compressing the rubber. A special lid fits over this assembly and when tightened, compresses the rubber between the two rings on top of the slips. When the rubber is compressed the wellhead is then packed off and no pressure can escape this connection. Water is then injected from the surface through the tubing and isolated below the packer leaving an annular space between the tubing and the production casing above the packer which can be accessed through the wellhead connections. This annulus between the casing and tubing must be periodically checked to ensure the mechanical integrity of the annulus above the packer.
State regulations address required Mechanical Integrity Testing (MIT) of this annular space in their Underground Injection regulations intended for fresh water zone protection. For example, the State of Texas requires in Section 3.9 Rule 9. DISPOSAL WELLS (Amended Effective April 1, 1982) Paragraph (11) TESTING.
(A) Before beginning disposal operations, the operator shall pressure-test the long string casing. The test pressure must equal the maximum authorized injection pressure or 500 psig, whichever is less, but must be at least 200 psig. PA1 (B) Each disposal well shall be pressure-tested in the manner provided in subparagraph (A) of this paragraph at least once every 5 years to determine if there are leaks in the casing, tubing, or packer. The Director may prescribe a schedule and mail notification to operators to allow for orderly and timely compliance with this requirement. PA1 The following pressure test shall be performed on Class II UIC Wells to establish the internal mechanical integrity of the tubing, casing and packer of the well. The permittee shall contact the District Office in which the well is located at least twenty-four (24) hours prior to conducting a pressure test to enable an inspector to be present when the test is done . . . PA1 1) Pressure Test
According to the Railroad Commission of Texas that once the starting test pressure is stable, a 10% variation from initial pressure is allowed throughout a 30-minute test interval in order to pass the Mechanical Integrity Test (MIT).
Under the State of Illinois requirements outlined in 62 ILLINOIS ADMINISTRATIVE CODE .sctn. 240.780 Reporting Requirements for Class II UIC Wells subpart g) Pressure Test:
The casing-tubing annulus above the packer shall be tested under the supervision of the Department at a minimum pressure differential between the tubing and the annulus of 50 PSIG for a period of 30 minutes. In addition, the casing-tubing annulus starting pressure shall not be less than 300 PSIG and may vary no more than five (5) percent of the starting test pressure during the test. The well may be operating or shut in during the test. PA2 There is large proportion of underground injection/disposal wells that will not pass the required state tests due to casing holes, thread leaks, packer leaks, etc. The most commonly used and the most widely accepted method of repairing casing holes is cement squeezing. Hydraulic cements such as Portland or pozzolan cements are typically used in this type of application. The composition of the cement slurries which are blended incorporate water, a hydraulic cement, and an endless array of possible additives to alter the properties of the cement for individual applications. When cement is emplaced against a porous medium i.e. earth strata, the cement loses water into the porous medium. When a significant amount of water or filtrate loss occurs, the cement characteristics degrade, resulting in poor quality or even possible failure of the cement to repair the casing section. In addition, the process is expensive. Other commonly used applications include polymer crosslinking by applying a solute crosslinking ion such as chrome, boron, titanium, etc. into a solvent of polymer consisting of guar, xanthan gum, HEC, CMC, PHPA, polyacrylamides, etc. and pumping the solution into the annulus allowing the crosslink to develop into a gelled solution that effectively plugs the annulus and prevents fluid flow inward or outward to the casing. Additional methods include simple injection of gellable solutions, calcium carbonate in graduated sizes, and even in some cases, basic food-grade cornmeal which enlarges as it absorbs water. PA2 A practical economical method is needed to patch casing leaks on injection wells that requires no work-over rig, that sacrifices no hole diameter, that inhibits corrosion, that will not jeopardize packer retrieval, and most importantly, quickly and effectively, restores mechanical integrity to those existing wells to allow them to pass MIT.
______________________________________ DESCRIPTION OF RELATED PATENT ART INVENTOR DATE PAT. NO. DESCRIPTION ______________________________________ Baker et al. 1984 4,462,836 Cement Composition Roark et al. 1987 4,706,755 Fluid Loss Control Burdge et al. 1988 4,730,674 Plugging A Tubing/ Casing Annulus Bennett et al. 1988 4,754,810 Method For Patching Casing Leaks Kirkland et al. 1988 4,784,693 Cementing Composition Cowan 1991 5,016,711 Cement Sealing Cowan et al. 1991 5,020,598 Process For Cementing A Well Himes et al. 1993 5,191,931 Fluid Loss Control Method Johnson et al. 1993 5,228,524 Fluid System for Controlling Fluid Losses Cowan 1994 5,275,654 Cement Sealing Cowan 1996 5,484,020 Remedial Wellbore Sealing ______________________________________